The ever increasing amount of air traffic has caused a marked increase in the workload of flight crews and air traffic controllers in high traffic density areas around airports. The Next Generation (NextGen) overhaul of the United States airspace system and the companion Single European Sky ATM Research (SESAR) overhaul of the European airspace system create various trajectory-based mechanisms to improve air traffic management on those continents. Some solutions include the increased use of time-based requirements including time-based aircraft spacing and separation in high traffic density areas.
These new requirements are among the many time-based requirements placed upon a crew during a flight. In reality, every operation or maneuver of the aircraft depends on time. Some examples include:                1. A mutual required time of arrival (RTA) to be accepted between air traffic control (ATC) and the aircraft to economize the space and increase the flow of the aircraft flying into and out of airports.        2. On approach and landing using time-base separation (TBS) relative to the preceding aircraft to avoid wake turbulence of the preceding aircraft.        3. All aircraft that fly as formations regardless of mission need to meet at different points in air at a prescribed time, adhere to a schedule and report or arrive at certain points at a particular time.        4. An aircraft may be required to report to an air-to-air refueling rendezvous at a particular point in air at a particular time.        5. ATC commands an aircraft to report to or hold at a certain altitude for a certain time or duration        6. The aircraft may be required for a certain time to stay within a thrust climb rating for noise abatement.        
These and many more such time-based requirements demand the crew monitor the time and manipulate flight and thrust controls to achieve a result at the stipulated time. Currently existing human interfaces do not provide sufficient situational awareness of the time element and leaves achieving a result to the analysis and assumptions of the crew. In certain cases if the aircraft reports earlier or later, the operation of other aircraft may be affected. Above all, the SESAR and the NextGen initiatives work towards the twin economic aspect of space and fuel optimization. Both these can only be achieved by saving time or by following and adhering strictly to a time element. Therefore there exists a need to provide a situational awareness of a time-based control to the crew to monitor the possibility of achieving a required activity in accordance with the time-based control.